Abstract
To investigate the formation characteristics of hydrocarbon compounds during the maturation of type III kerogen, particularly focus on liquid products and late gas generation mechanisms—areas that have received relatively little attention in previous research. Utilizing parallel semi-open exothermic simulation experiments conducted at twelve different temperatures, this research delineates a model for hydrocarbon evolution by analyzing cumulative production and net increment of expelled and retained liquid hydrocarbons along with gaseous products. Additionally, it examines the compositional characteristics of heavy molecular weight hydrocarbons (C15+) within liquid hydrocarbons. The findings categorize hydrocarbon generation and expulsion into distinct stages: Immature stage (300 ∼ 360 ℃): This stage primarily produces residual liquid hydrocarbons, with yields ranging from 0.24 mg/g to 0.32 mg/g. Mature stage (360 ∼ 440 ℃): Rapid cracking of kerogen and asphaltenes occur, resulting in substantial production and discharge of liquid hydrocarbons. Expelled oil increases significantly from 0.30 mg/g to 2.83 mg/g. High maturity stage (440 ∼ 500 ℃): At this point, secondary cracking begins for liquid products; total yield decreases from 3.67 mg/g to 2.94 mg/g while generating considerable amounts of heavy hydrocarbon gases (C2-C5). Secondary cracking stage for heavy hydrocarbon gases (500 ∼ 590 ℃): In this final stage, heavy hydrocarbon gases yield declines from 1.03 mg/g to 0.71 mg/g, whereas methane—the primary product—exhibits variability in yield between 2.08 mg/g and 2.71 mg/g. These results contribute valuable insights into the complex processes governing hydrocarbon generation during kerogen maturation. The REPI index of liquid hydrocarbons during the oil generation stage increases from 0.06 to 0.47, while the ISI value decreases from 0.067 to 0.007. This trend suggests a continuous rise in the gas potential of liquid hydrocarbons at this stage. Conversely, the ISI index for the gas generation stage rises from 0.007 to 0.2, indicating that residual liquid hydrocarbons contribute to the late stages of gas generation and that overall gas generation potential is declining. The findings presented above hold significant theoretical implications for understanding the hydrocarbon generation characteristics associated with type III kerogen cracking and elucidating the mechanisms underlying late-stage gas generation from liquid hydrocarbons.
Paper Information:
Junjie Xiao, Ziqi Feng*, Zhen Qiu, Qin Zhang, Yangming Li, Wei Wang, Mingxiang Yang, 2025. Formation mechanism of liquid hydrocarbon products of type III kerogen: Insights from temperature-based semi-open pyrolysis. Fuel 391, 134642. https://doi.org/10.1016/j.fuel.2025.134642.
